Dynamic OD transit matrix estimation: formulation and model-building environment

The aim of this paper is to provide a detailed description of a framework for the estimation of time-sliced origin-destination (OD) trip matrices in a transit network using counts and travel time data of Bluetooth Smartphone devices carried by passengers at equipped transit-stops. A Kalman filtering formulation defined by the authors has been included in the application. The definition of the input for building the space-state model is linked to network scenarios modeled with the transportation planning platform EMME. The transit assignment framework is optimal strategy-based, which determines the subset of paths related to the optimal strategies between all OD pairsPeer ReviewedPostprint (author’s final draft

A computational comparison of two simplicial decomposition approaches for the separable traffic assignment problems : RSDTA and RSDVI

Draft pel 4th Meeting del Euro Working Group on Transportation (Newcastle 9-11 setembre de 1.996)The class of simplicial decomposition methods has shown to constitute efficient tools for the solution of the variational inequality formulation of the general traffic assignment problem. The paper presents a particular implementation of such an algorithm, called RSDVI, and a restricted simplicial decomposition algorithm, developed adhoc for diagonal, separable, problems named RSDTA. Both computer codes are compared for large scale separable traffic assignment problems. Some meaningful figures are shown for general problems with several levels of asymmetry.Preprin

Comparison of the crack pattern in accelerated corrosion tests and in finite elements simulations

In this work, the crack pattern obtained in accelerated corrosion tests is compared to the one obtained in numerical simulations for reinforced steel concrete samples. In the simulations, an expansive joint element is used to simulate the oxide layer behaviour together with finite elements with embedded adaptable cohesive crack to simulate the concrete fracture. In parallel, some samples are artificially corroded imposing constant current and after corrosion they are impregnated with resin containing fluorescein to improve the detection of the cracks. In the paper, the main features of the model and the experimental procedure are described and the crack pattern is analysed. A main crack across the concrete cover is easily seen in both cases, but also secondary cracks are observed after treating the concrete surface, in accordance with the model predictions, which gives further support to the ability of the numerical approach to simulate the real cracking processes

Dynamic user equilibrium on traffic networks. An analysis and a discretized model

This paper formulates a discretized version of the Dynamic User Equilibrium problem on traffic networks as a variational inequality problem with special emphasys on the traffic dynamics. A finite difference approximation to the simple continuum model is generalized to the case of a multidestination network, giving to the resulting model a bilivel programming structure and an heuristic algorithm is outlined to solve the model.Peer ReviewedPostprint (published version

An heuristic algorithm for dynamic network loading

This paper describes an heuristic procedure for the problem of determining the time evolution of traffic flows and routes on a road net work with the key requirement that its computational costs must be appealing so as to include it as part of a real time Traffic Management System.Peer ReviewedPostprint (published version

Determination of the bilinear stress-crack opening curve for normal- and high-strength concrete

An improved version of the method proposed to ACI committee 446 and to RILEM TC 187-SOC to determine the fracture parameters of concrete is applied in this study to several mixtures of normal and high-strength concretes. The results are processed with a C++ program developed by the authors to automatise the mathematical operations required to obtain the bilinear softening curve of concrete from the experimental results. Numerical simulations of the tests are also carried out using finite elements with an embedded cohesive crack. The comparison between numerical and experimental results confirms that the experimental and numerical procedures are appropiate for normalstrength concretes and high-strength concretes

A Recursive Bateson-Inspired Model for the Generation of Semantic Formal Concepts from Spatial Sensory Data

Neural-symbolic approaches to machine learning incorporate the advantages from both connectionist and symbolic methods. Typically, these models employ a first module based on a neural architecture to extract features from complex data. Then, these features are processed as symbols by a symbolic engine that provides reasoning, concept structures, composability, better generalization and out-of-distribution learning among other possibilities. However, neural approaches to the grounding of symbols in sensory data, albeit powerful, still require heavy training and tedious labeling for the most part. This paper presents a new symbolic-only method for the generation of hierarchical concept structures from complex spatial sensory data. The approach is based on Bateson's notion of difference as the key to the genesis of an idea or a concept. Following his suggestion, the model extracts atomic features from raw data by computing elemental sequential comparisons in a stream of multivariate numerical values. Higher-level constructs are built from these features by subjecting them to further comparisons in a recursive process. At any stage in the recursion, a concept structure may be obtained from these constructs and features by means of Formal Concept Analysis. Results show that the model is able to produce fairly rich yet human-readable conceptual representations without training. Additionally, the concept structures obtained through the model (i) present high composability, which potentially enables the generation of 'unseen' concepts, (ii) allow formal reasoning, and (iii) have inherent abilities for generalization and out-of-distribution learning. Consequently, this method may offer an interesting angle to current neural-symbolic research. Future work is required to develop a training methodology so that the model can be tested against a larger dataset

Modelling of non-uniform corrosion-induced cover cracking in reinforced concrete

Cover cracking and spalling in concrete due to corrosion of reinforcement bars is one of the major concerns for durability of reinforced concrete structures and has been widely researched during recent years. Most approaches to the problem are based on a uniform corrosion and expansion pressure around the rebar. However, corrosion rust tends to accumulate around the steel circumference that faces the concrete cover. From this outer part of the rebar, the corrosion front gradually advances to the inner, which entails a non-uniform expansive pressure around the rebar. The purpose of the study is to simulate the effect of non-uniform rust distribution around the corroded rebar, taking advantage of an embedded cohesive crack finite element. The objective is to develop more realistic models for the estimation of the service life of reinforced concrete structure